The present invention relates to night vision systems of the type disclosed in commonly-owned U.S. application Ser. No. 707,224, filed on Mar. 1, 1985, which permit vision under low light conditions by intensifying incoming infrared and/or visible light from an object and converting it to an intensified visible light. The invention has particular application to night vision systems of the binocular goggles type, which can be mounted on a viewer's head covering his eyes. One of the main applications of night vision systems are military in nature, and the goggles of the present invention is intended, as one of its main uses and applications, for aircraft pilots, though myriad other uses are possible and practicable, such as police, fire, commercial aviation applications, military aircraft, and night-blind people.
Existing night vision goggles are heavy, cumbersome and unstable. They do not even resemble common goggles, but rather resemble television cameras mounted on the viewer's head, protruding more than 175 mm from the viewer's eye, and weighing as much as 850 grams. The weight and front-to-back length of such systems exert large moments on the viewer's head, causing serious instability problems and preventing effective use of the systems in applications where the head is subjected to gravitational or centrifugal loads.
Night vision systems typically include an objective lens set, an image intensifier and an eyepiece lens set, all arranged in a straight line. The lens design may be such as to result in an inverted image at the viewer's eye. Correction of this condition by the addition of a further inverting lens set would only add to the already excessive length of the system, aggravating the instability problem. Accordingly, the condition is corrected by the use of twisted fiber optics in the intensifier. But such twisted fiber optics have a greater overall optical length, result in a more costly image intensifier and impair the registration or alignment of the two binocular channels.
Additionally, existing night vision goggles cannot handle sudden excessive lighting conditions, such as flares or other bright lights. In such conditions, the goggles become inoperative and must be turned off. When the intensifier is turned off, most prior systems become opaque, rendering the viewer essentially blind. It is known to provide night vision goggles wherein the main optical assembly is coupled to the user's eye through a periscope-type arrangement, the reflection to the viewer's eye being provided by a beam splitting prism which is transparent when the system is turned off, permitting the viewer to look past the main optical assembly. But such arrangements still suffer from all of the other disadvantages discussed herein.
Furthermore, prior systems have an extremely limited field of view with little or no peripheral vision. This renders such systems essentially useless for applications requiring peripheral vision, such as in police work where the viewer is driving an automobile or other vehicle, and must be able to view the instrument panel without significant head movement.